60 solved GATE CS questions on Databases, drawn from 9 exam years and grouped by year. Every question shows the official answer and a step-by-step solution.
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Revision companion
Connect database definitions to small, checkable calculations. Start with stated constraints, not a pattern remembered from another question. Record the schema, dependencies, duplicate semantics, or transaction order before choosing a rule. These selected revision notes are a starting point, not a complete syllabus.
Our study notes and original examples support the PYQs below; they are not official exam questions or a replacement for the current syllabus.
Compute X+ by starting with X and repeatedly applying dependencies whose left sides are included, until nothing changes. X is a superkey when its closure contains every attribute; a candidate key additionally has no proper subset that is a superkey.
Check yourself: Can removing one attribute from your proposed key still determine the relation?
For every nontrivial dependency X → A, BCNF requires X to be a superkey. Third normal form also permits A to be prime, meaning it belongs to some candidate key. Check lossless join and dependency preservation separately; neither label substitutes for the other.
Check yourself: In a binary decomposition, does the shared attribute set determine either component?
Relational algebra uses sets; SQL normally retains duplicates. Joins can multiply rows through multiple matches. WHERE retains only TRUE, so NULL comparisons need care. COUNT(column) ignores NULL values; COUNT(*) counts rows. DISTINCT changes multiplicity, not the join condition.
Check yourself: Can you enumerate the joined rows before grouping or counting them?
Create one precedence-graph vertex per transaction. Add an edge for ordered operations from different transactions on the same item when either writes. Acyclicity establishes conflict serializability; a topological order supplies an equivalent serial order. It does not establish recoverability.
Check yourself: Have you excluded read-read pairs and checked every shared data item?
B+ trees support ordered traversal and ranges; hashing primarily supports equality lookup. An index lookup can still require data-page reads, especially for scattered matches. Calculate page accesses using index height, caching assumptions, and record layout rather than assuming an index eliminates I/O.
Check yourself: Could data-page access dominate the cost of this range query?
Original teaching example · not a PYQ
Original mini-example: R(A, B, C) is in 1NF, with dependencies generated only by A → B and B → C. Find its candidate keys, highest normal form among 1NF–BCNF, and a lossless BCNF decomposition.
Key: {A}. Highest normal form: 2NF. R1(A, B) and R2(B, C) are a lossless, dependency-preserving BCNF decomposition.
For the separate schedule r1(X), r2(X), w1(X), w2(X), with transaction subscripts, is conflict serializability satisfied?
No; the precedence graph contains a cycle.
r1(X) precedes w2(X), giving T1 → T2. r2(X) precedes w1(X), giving T2 → T1. These conflicting pairs form a cycle, excluding both possible serial orders.
Supplemental reading, not an official GATE reading list or an endorsement of these notes.
Free supplemental slides from the textbook authors covering relational design, SQL, indexing, and transactions. Revisit the relevant chapter after attempting questions.
This page shows 60 recent questions from the released archive, newest first. For older questions and complete papers, browse all GATE CS papers. Questions can carry more than one subject tag; counts are not marks weightage.
R(P, Q) and S(X, Y). Let…MCQ · +2 marks · MediumR(A, B, C, D). If and are the only two candidate keys of the relation , then…NAT · +2 marks · MediumR(A,B) and S(A,C): Relation R | A | B | |---|---| | 10 | 20 | | 20 | 30 | | 30 | 40 | | 30 | 50 | | 50 | 95 |…NAT · +1 marks · EasyPerson(pid, city), describes the city of residence for every person uniquely identified by pid. The following relational algebra…MCQ · +2 marks · HardStudent in a relational database. The primary key of this table is rollNum. | rollNum | name | gender | marks | |…NAT · +2 marks · EasyR(A, B, C, D, E) with the following three functional dependencies. AB → C; BC → D; C → E; The number…NAT · +1 marks · MediumR(P, Q, S, T, X, Y, Z, W) with the following functional dependencies.…MCQ · +2 marks · MediumRollNo.…NAT · +1 marks · HardP → QR RS → T Which of the…MSQ · +2 marks · MediumContinue learning with Success Tracker
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